1. Field of the Invention
The present invention relates to a multi-layer ceramic capacitor of which an internal electrode is constituted of a base metal, in particular, to a multi-layer ceramic capacitor of which an internal electrode is constituted of Cu.
2. Description of the Related Art
Multi-layer ceramic capacitors used in electronic devices such as portable devices and telecommunications equipment are exposed to a demand for smaller size and larger capacitance. As such a small size and large capacitance multi-layer ceramic capacitor, there is a multi-layer ceramic capacitor such as shown in for instance JP-A No. 2001-39765, of which an internal electrode is constituted of Ni. Since such the multi-layer ceramic capacitor is necessary to sinter in a reducing atmosphere, to a BaTiO3 base ceramic material that constitutes a dielectric ceramic layer, various additives are added to improve the reduction resistance. However, since, owing to addition of the additives, the sinterability of the ceramic material is deteriorated, a sintering temperature is set at a temperature of 1200° C. or more.
From the viewpoint of the energy efficiency, a multi-layer ceramic capacitor constituted of a material sinterable at a temperature such low as substantially 1000° C. is proposed. For instance, in JP-A No. 5-217426, a method where glass is added to lower the sintering temperature is proposed. However, when an additive amount of glass is increased to lower the sintering temperature, the permittivity is lowered; accordingly, a small size and large capacitance capacitor becomes difficult to obtain.
In JP-A No. 63-265412, a multi-layer ceramic capacitor that is constituted of a material that is capable of reducing and sintering at 1080° C. or less and has such high permittivity as 2000 or more is disclosed. In such multi-layer ceramic capacitor, Cu or an alloy mainly made of Cu can be used for an internal electrode. However, since the multi-layer ceramic capacitor uses Pb-perovskite type dielectrics in a primary phase of a dielectric ceramic layer, in recent lead-free tendency, there is a problem from the environmental point of view. Furthermore, JP-A No. 10-212162 discloses a multi-layer ceramic capacitor that is constituted of a lead-free material that can be sintered at 1080° C. or less. However, in the multi-layer ceramic capacitor, the permittivity is substantially 20 and lower than that of a BaTiO3 base material; accordingly, it is difficult to obtain a small size and large capacitance multi-layer ceramic capacitor.